Curl occurs in layered photoreceptors primarily since each layer has a different thermal contraction coefficient, or due to shrinkage during fabrication process. In particular, the charge transport layer usually has a higher contraction coefficient than the photoconductor supporting substrate. In forming the imaging member, the charge transport layer may be formed from a solution which is then heated or otherwise dried. As a result of the mismatch, the higher contraction coefficient causes the imaging member to curl as the imaging member cools from the higher drying temperature down to ambient temperature. The anticurl backside coating (ACBC) layer is applied to flatten or substantially flatten the substrate.
In embodiments, the photoconductors disclosed herein include an ACBC layer on the reverse side of the supporting substrate of a belt photoreceptor. The ACBC layer, which can be solution coated, such as for example, as a self-adhesive layer on the reverse side of the substrate of the photoreceptor, may comprise a number of suitable materials such as those components that may not substantially effect surface contact friction reduction and prevents or minimizes wear/scratch problems for the photoreceptor device. In embodiments, the mechanically robust ACBC layer of the present disclosure usually will not substantially reduce the layer's thickness over extended time periods to adversely effect its anticurling ability for maintaining effective imaging member belt flatness, for example when not flat, the ACBC layer may, but not necessarily will, cause undesirable upward belt curling which adversely impacts imaging member belt surface charging uniformity causing print defects which thereby prevent the imaging process from continuously allowing a satisfactory copy printout quality; moreover, ACBC wear also produces dirt and debris resulting in dusty machine operation condition. Since the ACBC layer is located on the reverse side of the photoconductor, it does not usually adversely interfere with the xerographic performance of the photoconductor, and decouples the mechanical performance from the electrical performance of the photoconductor.
Moreover, high surface contact friction of the ACBC layer against the machine, such as printers, subsystems can cause the development of undesirable electrostatic charge buildup. In a number of instances with devices, such as printers, the electrostatic charge builds up because of high contact friction between the ACBC layer and the backer bars which increases the frictional force to the point that it requires higher torque from the driving motor to pull the belt for effective cycling motion. In a full color electrophotographic apparatus, using a 10-pitch photoreceptor belt, this electrostatic charge build-up can be high due to the large number of backer bars used in the machine.
The present disclosure relates generally to electrophotographic imaging members, inclusive of photoconductors. More specifically, the present disclosure relates to photoconductors having enhanced durability, and as compared to a known polytetrafluoroethylene doped ACBC layer, a slippery surface, a higher bulk conductivity and excellent mechanical wear characteristics, and where the ACBC layer is located on the side of the substrate opposite that of the imaging layers. Also, the ACBC layer of the present disclosure possesses in embodiments resistance to airborne chemical contaminants, which can decrease the photoconductor service life. Typical chemical contaminants include solvent vapors, environment airborne pollutants, and corona species emitted by machine charging subsystems such as ozone. Further, the photoconductor in a xerographic system is subjected to constant mechanical interactions against various subsystems.
The ACBC layer in this disclosure can be a two layer or single layer structure. In the two layer structure, the bottom layer adjacent to the substrate provides anticurl functionality, and the top layer adjacent to the bottom layer provides wear resistance, slippery surface, and antistatic properties.
A number of backing layer formulations are disclosed in U.S. Pat. Nos. 5,069,993; 5,021,309; 5,919,590; 4,654,284 and 6,528,226. However, there is a need to create an ACBC layer formulation that has intrinsic properties that minimize or eliminate charge accumulation in photoconductors without sacrificing other electrical properties such as low surface energy. One ACBC design can be designated as an insulating polymer coating containing additives, such as silica or TEFLON®, to reduce friction against backer plates and rollers, but these additives tend to charge up triboelectrically due to rubbing resulting in electrostatic drag force that adversely affects the process speed of the photoconductor.